Antimony and tin are commonly used as principal alloying ingredients in a variety of lead-based alloys, such as, for example, as have been used in lead-acid cells and batteries.
Accordingly, the removal of tin, antimony, and other metals associated with lead becomes a primary consideration during the processing of lead-bearing materials, in particular, secondary sources of lead such as scrap lead, battery lead and lead drosses, so that refined soft lead can be obtained (the term "soft lead" simply referring to lead of sufficient purity so that it is soft and can be used for various alloys, as is known). More particularly, the demand for soft lead has been on the increase, spurred on, in part, by a shift in the battery industry over the years from the use of predominantly antimony-based lead alloys to calcium-based lead alloys and other non-antimony lead-based alloys. As is known, soft lead is needed to make calcium-based, lead-based alloys. The production of such soft lead involves extensive de-tinning and removal of antimony from lead bullion produced by secondary smelting of battery scraps, slags, drosses, baghouse dust or metallic scraps.
Traditional methods for extracting impurities and purifying lead from lead-bearing materials has often involved smelting the material in pyrometallurgical furnaces, such as a reverbatory, blast, rotary or electric furnace, followed by a variety of pyrometallurgical treatments to reduce the impurity levels in the lead to acceptable levels.
The tin, antimony and other impurities in the lead are typically captured in the dross or slag. Processing of drosses and slags is often handled differently depending upon the requirements of the processing plants.
Some plants strive to recover the metal values by selective oxidation and reduction practices via process pyrometallurgy. A typical example is the type of process in which impurities such as tin, antimony, arsenic, or tellurium are removed as salt melts by pyrometallurgic techniques. This treatment is then followed by a hydrometallurgical treatment to recover the metal values. The main disadvantages of this type of process are that such processes are extremely labor and capital intensive, typically requiring the consumption of expensive reagents such as caustic soda and sodium nitrate.
In some plants, drosses can also be smelted separately; and the alloy product resulting used as a master alloy additive. However, the presence of high levels of both tin and antimony in the dross could make this approach less appealing.
An alternative approach which has been used involves the drossing out of tin and antimony from the lead stream at one stage of the process to obtain soft lead. The dross is then recycled back into the metallurgical furnace system. However, this option, when combined with processing of fresh antimony and tin-based alloy feed materials through the metallurgical furnace system, has the effect of driving the impurity levels in the lead bullion higher, thereby increasing the quantity of dross in circulation.
The impact of this approach results in longer processing times, reduced equipment life, higher levels of reagent consumption, and higher smelter costs per time of process lead. Consequently, periodic purges would be required to reduce the impurity levels and the level of the dross in circulation. Disposal of the dross is not an attractive option because of potential environmental concerns. Likewise, the cost of disposal of such dross can tend to be prohibitive. Additionally, and still further, the economic value of the metals tied up in the dross would be thereby lost.
Other disadvantages of a pyrometallurgical approach of this type include the relatively high temperatures involved and the vast expenditure of energy required to accomplish the reactions. Similarly, the emission of hazardous fumes, gasses and dust can result; and the production of the slag which results is expensive to dispose of due to environmental constraints.
There is certainly a substantial need to provide an effective process for dealing with the problem discussed herein. However, despite the work that has been carried out, a satisfactory solution is not believed to have been provided.
Accordingly, and in general, a principal object of the present invention is to provide a facile method of treating alloys or drosses containing lead and other metallic impurities to separate and recover the metal components. A more specific object lies in the provision of a hydrometallurgical method to solubilize and effect separation of the metal components so as to allow recovery thereof.
Yet another object of the present invention provides an economic process for separating the metallic components from a dross or alloy source. A more specific and related object lies in the provision of a method in which fuel costs used are minimized, lower working temperatures can be utilized, and the apparatus requirements are relatively small in comparison to pyrometallurgical process requirements.
A still further and more specific object is to provide a hydrometallurgical treatment which allows, if not effectively eliminates, the emission of lead fumes and volatile dust and substantially reduces the emission of sulfur oxide gasses.
Another object of the present invention is to provide a process which can be utilized in connection with existing processes, such as processes utilizing pyrometallurgy, so as to provide efficient processes with minimal additional capital investment.
Yet another object provides a method compatible with other known pyrometallurgical or hydrometallurgical processes to allow recovery of the metal values resulting from the present invention.
Other objects and advantages of the present invention will become apparent as the following description proceeds, taken in conjunction with the accompanying drawings.